Pulse echo system



April A. PRElSMAN 2,419,590

PULSE ECHO SYSTEM Filed Feb. 2'7, 1943 2 Sheets-$heet 1 msifl k I 7 fizz I 14 J0 sconce- 24 g sv/v. paws 16 PULSE oarPz/r April 29, 1947- A. PREISMAN 2,419,590

PULSE ECHO SYSTEM Filed Feb. 27, 1943 2 Sheets-Sheet 2 60 Q 19 ,J8 I 61 RFC osmmran RECEIVER 66 T 0474567276 (ma/1r aw 24 mP/nBLE mom 1 62 F DEV/CE P0165 as/vzmrok A I 54 AC. sums SWEEP A $9 GENE/W770i? SWEEP c/nw/r Manummk 1 PHASE L co/vmoL ELEMENT! muss 3 Z d 40 I I I I l 1 QE 'E: e 40 l INVENTOR.

HL BERT PIPE/SMHN BY 7 K ATTORNEY Patented Apr. 239, 1947 NKTED STTES F F l C E PULSE ECHO SYSTEM Application February 27, 1943, Serial No. 477,394

.6 Claims. 1

This invention relates to radio systems and more particularly to the generation of a pulse of variable width for use in radio and other electrical systems.

The invention disclosed herein may be manufactured and used by or for the Government of the United States for governmental purposes without payment of any royalty thereon.

One of the objects of this invention is to provide a method and means to produce a pulse of a variable width or duration in which the leading edge thereof is adapted to be timed substantially in coincidence with a given point such as determined by a synchronizing pulse and which has a trailing edge portion adaptable as a marker.

Another object of this invention is to provide a method and means to produce a reference marker for an oscillograph of a radio detection system wherein the marker is adjustable relative to a reference point such as the transmission instant of an impulse to determine the time interval between such point and an echo pulse of the impulse with which the marker is adapted to be brought into coincidence.

Still another object of this invention is to provide a method and means of producing a pulse of variable duration from either an alternating current or a direct current source.

The invention comprises a method of producing a substantially rectangular pulse of variable duration or width by first initiating in response to a synchronizing pulse or a predetermined potential produced by an alternating or variable current source, the building-up of a potential for the pulse. This provides a leading edge which is substantially in coincidence with the synchronizing pulse or other predetermined electrical force, causing the initiation of the potential build-up. The trailing edge of the pulse is produced by shunting the source of the pulse potential at a selected interval after the initiation of the pulse potential thereby producing a sudden potential drop. This shunting of the pulse potential source may be varied so as to vary the width of the pulse. This results in the production of a substantially rectangular pulse of variable width with the leading edge thereof predetermined in time.

More particularly, the method may comprise the control of the firing of first and second gasfilled tubes. The first gas-filled tube is caused to fire in response to a synchronizing pulse or a predetermined potential produced by an alternating or other current source ap'pliedthereto. The output of the first tube is applied across a resistor, the potential across which is in turn applied to the second tube to control its firing. The potential of the energy applied to the second tube is controlled so that its requires a predetermined time interval before it can approach the potential across said resistor. The control of the firing of the second tube also includes control of the bias thereof. The firing of the second tube operates to shunt said resistor, the main portion of the output energy of the first tube being conducted by the second tube reduces the potential across said resistor thereby defining the trailing edge of the pulse.

The variable width pulse thus produced is particularly useful as a marker for the oscillograph of a radio detection system. A further feature of the invention therefor comprises synchronizing the generation of the variable width pulse with the transmission of impulses. By varying the width of the pulse, the trailing edge thereof can be used as a marker whereby the width of the pulse is directly proportional to the time interval between the transmission of an impulse and its echo when the trailing edge is brought into coincidence with the pulse produced by the echo on the oscillograph.

For a better understanding of the method and of an apparatus by which the method may be practised, reference is had to the following detailed description to be read in connection with the accompanying drawings, in which:

Fig. 1 is a schematic wiring diagram of the variable pulse generator in accordance with this invention;

Fig. 2 is a graphical illustration of the steps of producing and effecting variation of the variable width pulse;

Fig. 3 is a block diagram of a radio detection system incorporating the variable width pulse generator of this invention; and

Fig. 4 is a graphical illustration showing the application of the variable width pulse as a marker for the oscillograph of the radio detection system.

Referring to Fig. 1, the variable width pulse generator 8 of this invention is shown comprising first and second gas-filled tubes I0 and I2 which preferably are of the type known under the trade mark Thyratron. By way of example the tubes I0 and I2 may be types 2050 and 884 respectively. The tubes [0 and I2 comprise anodes l4, l5, grids I6, I! and cathodes l8, l9 respectively. The anode l-t of the tube I0 is connected to a resistor R1 and a variable condenser C1 arranged in parallel. To the opposite side of the resistor R1 is a connection 2|] between which and ground 2| is supplied a source of power which may be either direct current or alternating current. The grid I6 of the tube I is provided with an input circuit 24 having a condenser 25 and a biasing resistor 26.

Where direct current is applied as the operating power for the generator, the grid I6 is biased so that a source of synchronizing pulses applied to the input connection 24 will serve to control the firing of the tube I0. Extinguishment of the firing of the tubes may be accomplished by applying thereto a negative extinguishing pulse or by opening the plat circuit of the tube I0.

Where alternating current is applied to the generator the grid I6 may be biased, if desired, to cause the tube It to fire of its own accord at a selected potential on the positive half of an alternating current cycle occurring some place between zero and the crest thereof. Preferably, the grid I6 is biased so negatively that the tube will not fire in response to an alternating or other varying potential unless the grid is triggered by a synchronizing pulse.

The terminal 30 of the cathode I8 is connected by a line 3i to the anode I of the tube i2 and to the output connection 32 of the generator. Also connected to the cathode terminal 30 is a potentiometer R2 having a movable tap 35 which is connected to the cathode IQ of the tube I2. By this potentiometer connection the bias of the tube I2 can be controlled. Connected to the terminal 30 by means of the line 3| is an integrating circuit 36 comprising a variable resistor R3 and a condenser C2. The voltage passing through the integrating circuit 36 is applied direc vly to the grid H of the tube I2.

When the first tube i0 is caused to fire, say at the crest of an alternating current applied to the line 20, a current will flow through the resistance R4, the tube l0 and the potentiometer resistance As indicated in Fig. 2, this produces a pulse potential .40 across resistance R2 having a wave front M which is in substantial coincidence with a synchronizing pulse 39 applied to the grid I6. The resistance values of R1, the tube I0 and R2 determine the current flow and therefore the amplitude 42 of the pulse potential. This amplitude 42 would normally be maintained until the alternating current supply voltage drops below a value necessary to maintain the ionization of the tube I0. For purposes of illustration, this point on the alternating current wave 44 may be taken as a point 45.

The trailing edge and therefore the variable width characteristic of the pulse 43 is controlled by the operation of the second tube I2. The integrating circuit 36 provides a time constant which controls the potential build-up on the grid IT. The rate of the build-up of the control potential on grid Il depends upon the values of the resistor R3 and condenser C2. This rate of buildup may be represented by a curve 35 (Fig. 2).

While I have shown resistor R3 as variable and condenser C2 as fixed it will be understood that either or both these elements may be made variable. By varying the value of the time constant of the circuit 35 the inclination of the curve 46 can be varied.

This increase in voltage from the circuit 36 is applied to the grid I! of the tube I2 whose cathode I9 is biased positively with respect to the grid I! by the location of the tap 35 on the potentiometer R2. When the voltage applied to the grid I! rises to the bias determined by the locaof the condenser C1.

tion of the tap 35 the tube I2 fires. The firing of the tube I2 reduces the resistance of the circuit through the tube from the line 3| to the cathode I9 thereby providing in effect a shunt across the portion of the resistance R2 between the terminal 3!) and the tap 35. This shunting action reduces the potential at the terminal 30 and hence at the output 32 from the original amplitude 42 to a lower amplitude 52, a value determined largely by the ionization potential of the tube I2. This accounts for the sudden voltage drop 53 of the pulse 40 (Fig. 2). Since the resistor R1 is in series with the tubes I0 and I2, and preferably is large, that is, about 30,000 ohms more or less, it operates to limit the current to a safe value. When the alternating current supply drops below the sum of the two extinguishing potentials of the tubes 10 and I2 the tubes go out and the system waits until the next positive crest of the alternating cycle reoccurs.

The shape of the leading edge 4| of the pulse 50 may be controlled by varying the adjustment For one adjustment the leading edge may be caused to extend above the amplitude level 42 as indicated by the broken lines l6 (Fig. 2) or the condenser may be adjusted to provide a right angle corner for the pulse as indicated or further adjusted to round it off.

It will be clear from the foregoing description that the trailing edge portion 53 and therefore the width of the pulse depends upon the moment when the tube I2 fires. The firing of the tube I2 can be controlled either by varying the cathode bias, that is, by moving the tap 35 along the length of the potentiometer R2 or by varying the rate of rise of the voltage applied to the grid ll, that is, by varying the time constant of the integrating circuit 36.

In Fig. 2, the value on the curve 46 indicated by the broken line -I is the bias value selected by the position of the tap 35 and determines the firing of the second tube I2 to produce the trailing edge 53. Should the time constant of the circuit 36 be varied to a value represented by the curve 46a, the same bias value I will produce a trailing edge 530. thus producing a pulse of greater width. Should the potentiometer tap 35 be moved to a different position such as indicated by the value 2 this value for the curve 46 will produce a pulse width indicated by the line 54, and for the curve 46a the value 2 will produce a pulse having a width indicated by the line 54a.

If the integrating circuit 36 is made of high enough time constant so that the curve 46 has a rise which is substantially linear for the interval between the synchronizing pulse 39 and the point 45, the firing of the tube I2 and hence the width of the output pulse 40 will vary in substantially direct proportion to the variation of the bias of the cathode I9. This feature of the invention is of practical utility for determining the time interval between a transmitted impulse and an echo thereof in radio detection systems. The usual potentiometer pointer corresponding to the tap 35 may be used as a direct reading of the time interval between the transmitted impulse and a particular echo with which the trailing edge of the pulse 40 coincides thus giving the distance to the obstacle causing such echo.

If the synchronizing, signal varies in its timing from one cycle to the next, the moment of initiation of the marker pulse varies correspond.- ingly and as a consequence the plateau denoted by 52 in Fig. 2 varies in length. This in turn varies the residual charge on condenser 02 should any be permitted to remain from the preceding cycle, and such variation of residual charge would effect the operation and therefore the marker width during the next half cycle. To prevent the marker width from being a function of the synchronizing moment, it is necessary that condenser C2 be as nearly completely discharged before the initiation of the next marker pulse. This is accomplished by the direct connection from 36 to grid ll. Thus connected, the tube [2 can function during the negative half cycle of the power supply as an ordinary diode, and the condenser C2 will be discharged practically completely through the low resistance path made up of the resistance of the grid I1 and the cathode i 3 in series with the portion of resistance R2 between tap 35 and ground. It is to be noted that during this negative half cycle, the tube i2 is deionized so that the tube can function in the above-mentioned manner as a diode with the current flow in the direction from the grid to cathode which is the right polarity to discharge condenser C2.

In Fig. 3, I show a form of radio detection system similar to that disclosed in the copending application of E. Labin, Serial No. 473,310, filed J anuary 23, 1943, in which I have incorporated the variable width pulse generator of my invention. This system is supplied with alternating current and since the variable width pulse generator of this invention can operate on alternating current, it is particularly applicable as a marker for the oscillograph of the Labin system. The system comprises an impulse transmitter composed of a radio frequency oscillator 58, a pulse modulator 59 and an antenna 60 for transmission of recurring impulses. A receiver BI and a cathode ray oscillograph 52 are included to receive and indicate echo pulses caused by obstacles in response to the transmission of impulses. Connecting the output of the pulse modulator 59 to the receiver BI is the usual blocking circuit 63 arranged to block the receiver during the transmission of impulses, The sweep generator 64 is connected to the output of the modulator 59 whereby a sweep potential A-B is provided for the oscillograph in synchronism with the transmission of impulses. The variable width pulse generator 8 of Fig. 1 is connected in the system with the grid connection 24 connected to the output of the modulator 59 so that pulse energy in accordance with the transmission of impulses is received for synchronizing the operation of the generator. An alternating current source 68 is applied directly to the oscillator 58 and the modulator 59. A phase control 69 controls the alternating current applied to the receiver 6] and the sweep generator '64, the variable width pulse generator 8 and the oscillograph 62.

In Fig. 4, the crest M of the alternating current source is shown with a transmitted impulse l0 superimposed thereon to indicate the relation of the transmission of the recurring impulses and the cycles of the alternating current. For purposes of illustrating this invention, the impulse H1 is shown to have been transmitted shortly after the crest has been reached. It will be understood, of course, that the alternating current cycle is greatly reduced relative to the sweep A-B in the drawing for illustration purposes. In actual practice the sweep interval A-B will be about 500 microseconds, and where 60 cycle alternating current is used, this is about 3 per cent of one cycle. In order to provide a peak portion of the positive half of the cycle for the receiver during reception of a given range'A--B, the phase control 69 is adjusted to retard the alternating current by an angle 0. Thisis indicated by the broken line 44a.

The operating interval AB is shown to have three echo pulses at, y and 2 caused by obstacles in response to the impulse 18. The output of the generator 8 is applied to the vertical deflecting plates of the oscillograph so that the trace line of the oscillograph follows the outline of the pulse 4!! as shown in Figs. 2, 3 and 4. For the adjusted position illustrated for bias value I the trailing edge 53 of the pulse is caused to coincide with the first echo pulse :0. As indicated at 40, Fig. 4, the pulse as appearing on the oscilloscope is poised on the corner of the pulse directly above the trailing edge 53. For this position of adjustment, the time interval i1 is obtainable from the setting of the potentiometer R2. Should the interval is be desired for the location of the echo pulse y, the potentiometer will be adjusted until the trailing edge 53 lifts the pulse 1/ to the upper level of the pulse as indicated at 4d. Like- Wise, the time interval is to the echo pulse a may be obtained by a further adjustment of the potentiometer until the pulse a is lifted above the trailing edge 53 as indicated at 4e. It will therefore be clear that the marker feature provided by the variable width pulse generated in accordance with my invention provides for determining the time interval to a particular echo pulse and therefore the distance to the obstacle causing such pulse. Further, the variable width pulse output of the generator 8 is satisfactory for most purposes without the need of subsequent amplificaion.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects thereof and the accompanying claims.

What I claim is:

1. A method of producing a reference marker for the cathode ray oscillograph of a radio detection system wherein an impulse is transmitted and echoes thereof are detected by their deflection of the cathode ray comprising initiating the building-up of a pulse potential in response to energy of said impulse, said pulse potential having its leading edge substantially in coincidence with the leading edge of said impulse, reducing the pulse potential at an interval after initiation thereof so as to produce a. potential drop, synchronizing the cathode ray sweep with said impulse, deflecting the cathode ray by said pulse potential to thereby define a marker thereon in accordance with said potential drop and controlling the length of said interval to efiect coincidence of said marker with a particular echo deflection of said cathode ray.

2. A pulse generator for producing a substantially rectangular pulse of selectable duration comprising first and second gas-filled tubes, said first tube including anode and cathode electrodes, a resistor in the anode-cathode circuit of said first tube, means including a. source of current to control the firing of the first tube to produce a potential across said resistor, said anode having in circuit therewith a resistance and a condenser in parallel connection to produce a sharp rise to a given value in potential across said resistor, means to apply energy of the potential across said resistor to said second tube to cause it to fire and thereby shunt said resistor, and means controlling the application of said potential to delay the firing of said second tube a time interval corresponding to the desired duration of saidpulse.

3. In a radio detection system having means to transmit an impulse and receiving means including an oscillograph to indicate echo pulses thereof, the sweep circuit of said oseillograph being synchronized to the transmission of impulses; the combination therewith of means for producing a marker for the oscillograph to determine the interval between the transmission of an impulse and an echo pulse thereof, comprising means synchronized to energy of said impulse to initiate at the transmission of the impulse the buildingup of a pulse potential, means responsive to said pulse potential to effect the building-up of a control potential, means controlled by said control potential to reduce said pulse potential at a selected interval after initiation thereof and thereby produce a drop in said pulse potential, and means to apply said pulse potentia1 to said oscillograph so as to define by means of the reduction in potential a marker locatable thereon in coincidence with said echo pulse.

4. The system defined in claim 3 in combination with a source of alternating current and means to supply the alternating current directly to the transmitting means, the receiving means and the marker producing means as the operating power therefor.

5. A pulse generator for producing from alterhating current substantially rectangular pulses of desired duration comprising first and second gas-filled tubes, said first tube including anode, grid and cathode electrodes, a resistor in the anode-cathode circuit of said first tube, means to apply alternating current across said anodecathode circuit, means to apply synchronizing impulses to said grid electrode to control the firing of the first tube to produce a pulse potential across said resistor for substantial coincidence with the controlling impulse, means connecting a source of current across said anode-cathode-resistor circuit, means to apply energy of said pulse potential to said second tube to cause it to fire and thereby shunt said resistor, means to control the length of the interval between the firing of the first and second tubes, and means controlling.

the anode-cathode circuit to produce a sudden build-up of potential to a given value across said resistor upon the firing of said first tube and to reduce said potential sharply upon the firing of said second tube.

6. A pulse generator according to claim 5 wherein the means for controlling the anodecathode circuit includes a resistance and a condenser in parallel connection connected to said anode.

ALBERT PREISMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

